Generally, a highly integrated semiconductor device is fabricated by a series of steps comprising:
forming a conductive thin film such as a metal film or the like as a conductive wiring material and an interlayer dielectric film for insulating between the conductive thin films on an element such as a silicon wafer, and then uniformly applying a photoresist onto the surface of the resultant to provide a photosensitive layer, which is subjected to selective exposure and development to form a desired photoresist pattern; then,
conducting dry etch treatment of the interlayer dielectric film using this photoresist pattern as a mask to form a desired pattern on the thin film; and,
completely removing the photoresist pattern as well as the residue resulting from the dry etch treatment (hereinafter, referred to as a “dry etch residue”) by oxygen plasma ashing, use of a cleaning solution, or the like.
Recently, along with more shrunken design rules, RC delay is becoming to get on top of the limitation of high-speed arithmetic processing. Accordingly, the interlayer dielectric film is making a shift from a silicon oxide film to a low-dielectric-constant interlayer dielectric film (a film with a dielectric constant of less than 3: hereinafter, referred to as a “low-dielectric-constant interlayer dielectric film”). Moreover, when a pattern of 0.2 μm or less is to be formed, a photoresist with a film thickness of 1 μm will result the aspect ratio of the pattern (a ratio obtained by dividing the thickness of the photoresist film by the line width of the photoresist) to be too large, causing problems such as destruction of the pattern. In order to solve this, a hard mask technique is sometimes employed, in which a film of a titanium (Ti) series, a silicon (Si) series or the like (hereinafter, referred to as a “hard mask”) is inserted between the pattern film that is to be actually formed and the photoresist film so as to first transfer the photoresist pattern onto the hard mask by dry etch. Once the photoresist is removed, this hard mask is used as an etch mask to transfer the pattern onto the film that is to be actually formed by dry etch. According to this method, since the gas used upon etching the hard mask is exchangeable with the gas used upon etching the film that is to be actually formed, one can select a gas that ensures selectivity between the photoresist and the hard mask upon etching the hard mask, and a gas that ensures selectivity between the hard mask and the film to be actually etched upon etching the actual film. Therefore, it is advantageous in that a pattern can be formed while causing minimum damage to the actual film.
Furthermore, since the current density of metal wiring has been increasing due to more shrunken design rules, a countermeasure is strongly required against electromigration, i.e., transport of a metal wiring material caused by the current flowing through the metal wiring material, which causes a hole in the metal wiring. As such countermeasures, there are methods in which cobalt or a cobalt alloy is formed as a cap metal on copper wiring, and methods in which cobalt or a cobalt alloy is used as a metal wiring material as described in Patent Literature 1. Accordingly, in addition to conventional copper wiring, cobalt and cobalt alloys have also become targets of damage suppression.
Accordingly, there has been a need for a method for removing a hard mask while suppressing damage to copper, copper alloys, cobalt and cobalt alloys upon fabricating a semiconductor device. In this regard, various techniques have been proposed.
Patent Literature 2 proposes a cleaning method that uses a cleaning composition comprising hydrogen peroxide, aminopolymethylene phosphonic acids, potassium hydroxide and water.
Patent Literature 3 proposes an etch composition having pH greater than 8.5 and comprising at least one selected from the group consisting of ammonia, a compound having an amino group and a compound having a ring structure containing a nitrogen atom, as well as hydrogen peroxide in an aqueous medium.
Patent Literature 4 proposes a cleaning composition comprising: a polar organic solvent selected from the group consisting of dimethylpiperidone, sulfones and sulfolanes; an alkali base selected from the group consisting of tetraalkylammonium hydroxide, choline hydroxide, sodium hydroxide and potassium hydroxide; water; a chelating agent or a metal complexing agent selected from the group consisting of trans-1,2-cyclohexanediamine tetraacetic acid, ethane-1-hydroxy-1,1-diphosphonate and ethylenediamine tetra(methylene phosphonic acid).
Patent Literature 5 proposes a method for cleaning a semiconductor device in which an aqueous sulfuric acid solution at 70° C. or higher is used for cleaning so that titanium nitride (TiN) film can be removed without etching cobalt (Co) silicide.
Patent Literature 6 proposes an etchant comprising a hexafluorosilicic acid compound and an oxidant.
Patent Literature 7 proposes an etchant comprising a halogen compound such as hydrochloric acid, an oxidant, and a metal layer anticorrosive selected from nitrogen-containing heteroaromatic compounds, quaternary onium compounds and the like.
Patent Literature 8 proposes an etch method in which an etchant comprising a fluorine compound such as hydrofluoric acid and an oxidant is applied to remove a layer containing titanium nitride (TiN) without removing a transition metal layer.
Patent Literature 9 proposes an etch method in which an etchant comprising an organic onium compound and an oxidant is applied to remove a layer containing titanium nitride (TiN) without removing a transition metal layer.
Patent Literature 10 proposes an etch method in which an etchant having pH of 1 or higher and comprising a specific fluorine compound selected from the group consisting of a metal salt of hydrofluoric acid and an ammonium salt of hydrofluoric acid, as well as an oxidant is used to preferentially remove a layer containing titanium nitride (TiN) rather than a layer containing a transition metal.